The Dutch government has an emergency alert system called NL-Alert. With this, they can send alerts to all cell phones in a region using the cell broadcast feature. So unlike SMS messages, everyone who has them enabled in the deployed region gets them immediately, even if the network is otherwise congested and without the government knowing the phone numbers in question.

As of iOS 7 the iPhone can now receive these alerts, as you can see with today's test in this Youtube video:

The air raid sirens in the background are nothing to worry about, they're tested every first monday of the month at noon.